agent mode has no tracking/progress comment, unlike tag mode -- a PR review run gives no signal it's started

createInitialComment (create-initial.ts) is only ever called from modes/tag/index.ts. modes/agent/index.ts explicitly opts out -- claudeCommentId: undefined // No tracking comment in agent mode, and its own header comment says it "bypasses the standard @claude mention checking and comment tracking used by tag mode."

track_progress doesn't add that comment to agent mode runs either. modes/detector.ts's detectMode forces the whole run into tag mode instead whenever track_progress is set on a pull_request/issues/issue_comment/pull_request_review_comment/pull_request_review event. So there's no way to get a progress comment on an agent-mode run (a mode: review-style automation call driven by `prompt`, say) without giving up everything agent mode does differently from tag mode.

For an automated PR review running in agent mode, there's currently no visible signal a run has even started until the final review (or a comment) lands, which for a review with CI-log inspection or a follow-up fix pass can be several minutes. No create-initial.ts placeholder, no sticky-comment target, nothing posted at all until the run's own final output.

Could agent mode get its own tracking-comment support -- gated behind track_progress (or a separate input, since forcing tag mode is presumably intentional for the existing input) -- without switching the run into tag mode? It wouldn't need feature parity with tag mode's mid-run edits, just something posted at start and updated once to reflect the final state, so a caller isn't silent for the whole run.